464 KOVUM OnGANUM. [fcOOX IT. 



tain degree of warmth when separated from the external atmo:? 

 plierc. Let an experiment be made, therefore with fibrous gub 

 stances of linen, and not of wool, feathers, or silk, which are 

 animal excretions. For it is to be observed that all powders 

 (where air is manifestly enclosed) are less cold than the sub 

 stances when whole, just as we imagine froth (which contains air) 

 to l^e less cold than the liquid itself. 



We have here no exactly negative instance, for we are not 

 acquainted with any body tangible or spirituous which does not 

 admit of heat when exposed to the fire. There is, however, this 

 difference, that some admit it more rapidly, as air, oil, and water, 

 others more slowly, as stone and metals. y This, however, bek rgs 

 to the table of degrees. 



No negative is here subjoined, except the remark that sparks 

 are not kindled by flint and steel, or any other hard substance, 

 unless some small particles of the stone or metal are struck ofT, 

 and that the air never forms them by friction, as is common!/ 

 supposed; besides, the sparks from the weight of the ignited 

 substance, have a tendency to descend rather than to rise, and 

 when extinguished becomes a sort of dark ash. 



We are of opinion that here again there is no negative; for 

 we are not acquainted with any tangible body which does not 

 become decidedly warm by friction, so that the ancients feigned 

 that the gods had no other means or power of creating heat; 

 than the friction of air, by rapid and violent rotation. On thu 

 point, however, further inquiry must be made, whether bodice 

 projected bv machines (as balls from cannon) do not derive sornn 

 degree of heat from meeting the air, which renders them some 

 what warm when they fall. The air in motion rather cools thai. 

 heats, as in the winds, the bellows, or breath when the mouth i.-&amp;lt; 

 contracted. The motion, however, in such instances is not sulli 

 ciently rapid f o excite heat, and is applied to a body of air, ami 

 rot to its component parts, so that it is not surprising that hea 

 should not be generated. 



Wo must make a more diligent inquiry into this instance ; for 

 herbs arid green and moist vegetables appear to possess a latent 

 heat, so small, however, as not to be perceived by the touch ir 

 single specimens, but when they are united and confined, so that 

 their spirit cannot exhale into the air, and they rather warm each 

 other, their heat is at once manifested, and even flame occasion 

 ally in suitable substances. 



ductor, and therefore not allowing the escape of heat. The confined 

 *iir is disengaged when these substances are placed under an exhausted 

 receiver. 



J This is erroneous. Air, in fact, is one ci tbe worst, and metal* 

 vs the best conductors of heat. 



